In recent years, in the field of automatically operated or automatic lathes such as numerical control (NC) lathes, to enable machining of much more complicatedly shaped workpieces from a bar-shaped worked material (hereinafter called a “bar”), compound or combination machining where a large number of types of tools including rotary tools are provided on a tool rest to enable diverse automatic machining such as milling in addition to turning is being promoted. Further, to shorten the machining time, various multifunction type automatic lathes carrying a plurality of (normally two) spindles and a plurality of (normally two to three) tool rests close together on a single lathe bed and capable of performing different types of machining (for example, outer circumferential turning and boring) simultaneously on the same bar or simultaneous machining on different bars have been proposed.
As this type of multifunction type automatic lathe, for example, there is known one provided with a main (or front) first spindle rotating while holding a bar supplied from outside the lathe, an auxiliary (or back) second spindle rotating while holding a partially machined bar received from the first spindle, and independently operating first and second tool rests equipped with pluralities of tools (for example, see Japanese Unexamined Patent Publication (Kokai) No. 10-315005 (JP10-315005A)). In this known automatic lathe, the first spindle, second spindle, first tool rest, and second tool rest operate along a plurality of independent control axes. Due to this, diverse automatic machining including simultaneous machining is performed.
Explaining this in more detail, the first spindle is configured to move linearly along a feed control axis (here, called the “Z1-axis”) parallel to its own axis of rotation. On the other hand, the first tool rest is configured to be located retracted to the side in the front of the first spindle in the axial direction and to move linearly along a feed control axis (here, called the “X1-axis”) perpendicular to the Z1-axis of the first spindle. The first tool rest is a so-called combtooth or gang tool rest holding a plurality of tools in a parallel arrangement and can mount a plurality of turning tools (or single point tools) in an arrangement enabling positioning perpendicular to the axis of rotation of the first spindle. Therefore, the first tool rest is capable of moving by interpolation the nose of a desired tool selected by indexing in accordance with an NC program by co-action between X1-axis motion of the first tool rest itself and Z1-axis motion of the first spindle. Due to this, the bar held in the first spindle is machined to the desired shape.
The first tool rest further has a feed control axis (here, called the “Y1-axis”) perpendicular to both the Z1-axis and X1-axis. The Y1-axis motion of the first tool rest is motion to index and select the desired tool. Further, the first tool rest may have mounted to it additional tools in a combtooth manner at other positions for selection by X1-axis motion and motion by interpolation by Y1-axis motion.
The second tool rest is located away from the first tool rest in front of the first spindle in the axial direction. The second tool rest is a rocking type tool rest holding a plurality of tools in an arc arrangement centered on a rotation indexing control axis (here, called the “I-axis”) parallel to the Z1-axis of the first spindle and can mount at the front holding portion drills or other drilling tools in an arrangement enabling positioning coaxially with the axis of rotation of the first spindle. Therefore, the second tool rest is capable of moving relatively linearly the nose of a desired tool selected by I-axis rotation in accordance with an NC program by Z1-axis motion of the first spindle. Due to this, the bar held in the first spindle is machined to be drilled in its end face.
The second tool rest further is capable of mounting similar drilling tools at a back holding portion at the opposite side to the front holding portion at the same positions as the plurality of tools for machining the bar held in the first spindle, coaxially but oriented in the opposite direction, to enable machining of a bar held in the second spindle. As opposed to this, the second spindle is configured having an axis of rotation parallel to the axis of rotation of the first spindle, located facing it coaxially in front of the first spindle in the axial direction, and moving linearly along a feed control axis (here, called the “Z2-axis”) parallel to the Z1-axis of the first spindle. Therefore, the second tool rest can move relatively linearly the nose of a desired tool oriented in the opposite direction in accordance with an NC program by Z2-axis motion of the second spindle. Due to this, end face drilling is performed on the bar held in the second spindle.
In this way, the above known automatic lathe can control the motion of the spindles and tool rests along four feed control axes in accordance with an NC program to simultaneously use as much as three tools selected on the two tool rests to automatically machine bars held at the two or front and back spindles. However, the tools mounted at the second tool rest cannot be moved by interpolation with respect to either bar held in the first and second spindles, so the type of machining able to be performed by the tools of the second tool rest is limited to end face drilling. Further, the tools which can be simultaneously used for the first and second spindles at the second tool rest are limited to a pair of tools mounted coaxially in opposite directions to each other, so the shapes of the holes which can be simultaneously machined inevitably are limited.
As another known multifunction type automatic lathe, there is one where, in addition to the configuration of the first spindle and first tool rest at the four-axis automatic lathe explained above, a second and a third tool rest are provided capable of moving tools by interpolation with respect to two bars held in the first and second spindles. In this multifunction type automatic lathe, the first spindle is configured to move linearly along the Z1-axis in the same way as the above four-axis automatic lathe. Further, the first tool rest is configured to move linearly along the X1-axis and Y1-axis in the same way as the above four-axis automatic lathe.
As opposed to this, the second tool rest is configured located away from the first tool rest in front of the first spindle in the axial direction and to move linearly along a feed control axis (here, called the “X2-axis”) perpendicular to the Z1-axis of the first spindle and a feed control axis (here, called the “Z2-axis”) parallel to the Z1-axis. The second tool rest is a so-called turret tool rest holding a plurality of tools arranged at equal intervals in the circumferential direction and can mount single point tools, drills, and other turning tools or milling cutters and other rotary tools in an arrangement enabling positioning radially or in parallel with the axis of rotation of the first spindle. Therefore, the second tool rest can move by interpolation the nose of a desired tool selected by indexing in accordance with an NC program by co-action between the X2-axis motion and Z2-axis motion of the second tool rest itself. Due to this, the bar held in the first spindle is machined to a desired shape. Note that the second tool rest has a rotation indexing control axis (here, called the “TI-axis”) parallel to the Z2-axis and selects tools by TI-axis rotation.
The second spindle is configured having an axis of rotation parallel to the axis of rotation of the first spindle, arranged to be able to face it in front of the first spindle in the axial direction, and moving linearly along a feed control axis (here, called the “X3-axis”) perpendicular to the Z1-axis of the first spindle and a feed control axis (here, called the “Z3-axis”) parallel to the Z1-axis. As opposed to this, the third tool rest has a configuration of a gang tool rest holding a plurality of tools in a parallel arrangement, mounts single point tools, drills, and other turning tools or milling cutters and other rotary tools in an arrangement enabling positioning parallel to the axis of rotation of the second spindle, and is located facing the X3-axis path of movement of the second spindle. Therefore, the second spindle can select the desired tool on the third tool rest by its X3-axis motion and move relatively by interpolation the nose of that tool in accordance with an NC program by co-action between the X3-axis motion and Z3-axis motion. Due to this, a bar received from the first spindle is machined to a desired shape.
Further, the first spindle and the second spindle may have rotation angle control axes (here, called the “C1-axis” and “C2-axis”). Therefore, the first and second spindles can use rotary tools mounted at the desired tool rests to perform diverse machining at desired positions on the end faces or outer circumferences of the bars held in them by positioning and indexing motions of the C1-axis and C2-axis.
In this way, the above known automatic lathe can control the motions of the spindles and tool rests along a large number of control axes in accordance with an NC program so as to simultaneously use as much as three tools selected on the three tool rests to automatically machine bars held at the two or front and back spindles. In particular, since it is possible to simultaneously perform individual motion by interpolation instructed for the three tools, there is the advantage that the bars can be machined to complicated shapes in a short time. However, the third tool rest for the second spindle is configured to be stationarily placed on the lathe bed, so to avoid interference between tool rests, the position of machining work by the third tool rest with respect to the second spindle is set to a position sufficiently away from the positions of machining work by the first and second tool rests with respect to the first spindle. As a result, the X3-axis motion of the second spindle becomes relatively large and, together with securing the installation space for the third tool rest, there is a tendency for the overall dimensions of the automatic lathe to increase.
Further, in the above automatic lathe, it is possible to use a special holder to mount tools given orientation to enable machining a bar held in the second spindle at a desired tool mount provided on the turret of the second tool rest. In this case, if mounting tools for machining a bar held in the first spindle given opposite orientations at the same tool mount, it is possible to perform automatic machining by the above three-tool simultaneous interpolation. However, with this configuration, the tools which can be simultaneously used with respect to the first and second spindles in the second tool rest are limited to a pair of tools mounted at the same tool mount on the turret, so the simultaneously machinable shapes are inevitably limited. Further, since the second tool rest is a turret tool rest, the time required for tool selection is longer than a gang tool rest and there is a concern that the effect of shortening the machining time by simultaneous interpolation will end up being canceled out.